Solar radiation has a spectral, or wavelength, distribution from short wavelength radiation such as gamma and X-rays, to long wavelength radiation such as long radio waves. Different regions of the solar spectrum can be described by the range of their wavelengths. The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation. About 99 percent of solar radiation is contained in the wavelength region from 300 nm to 3,000 nm. The visible spectrum extends from ultraviolet, about 390 nm, to near-infrared, 780 nm, and makes up only about 10 percent of the total solar spectrum. A peak in the solar spectrum occurs at 560 nm. The colour temperature of the solar spectrum varies with latitude between 3000 K and 3500 K.
It is difficult to utilise the full spectrum in the conversion of solar energy. For example, with parabolic reflector solar collectors, much of the solar energy is reflected back into space. Moreover, photovoltaic devices, used to convert solar energy, have a peak sensitivity at approximately 830 nm and only 14-16% of the collected energy is converted. Focussing rays of the sun using a multiplicity of mirrors to heat a liquid also results in much of the energy being reflected back into space.
U.S. Pat. No. 4,147,415 discloses a spiral shaped energy trap arranged so that incoming wave energy is reflected internally to reduce energy escape from the trap. There is no disclosure how trapped energy may be utilised within the trap or extracted from the trap, and the spiral shape would appear to provide difficulties in achieving such utilisation or extraction. Moreover, the spiral nature of the trap would appear to allow reversal and re-emergence of entrant energy waves.
U.S. Pat. No. 6,666,207 discloses a solar energy converter in the form of a cylindrical chamber with an input aperture in a centre of one circular end face. Since the motion of entrant energy may be expected to be substantially randomised by reflections, rather than circulating, a proportion of energy may be expected to re-emerge from the aperture. The cylindrical form also imposes limitations of energy utilisation within the chamber and extraction of energy from the chamber.
It is an object of the present invention at least to ameliorate the aforesaid disadvantages in the prior art.